72 



EXTERNAL CONFORMATION OF PLANTS. 



consists of two alternate (/. e. not opposite) leaves, the divergence of which is 

 alike -J- ; but the pairs themselves diverge from one another by smaller fractions. 



-Diafjram of a flower-stalk of Fritillaria inipe7-ialis, sliowiiif,' the diverg-ences of the first twenty-four foHag-e-leaves ; 

 the relative lengths of the internodes are indicated by the larger or smaller distances between the circles. 



If it is desired to unite all the leaves from 1-15 by a genetic spiral, an abrupt 



alteration of the divergence would 



be obtained within it. The relative 



positions are shown, however, 



more simply and clearly if, keeping 



in view the bilateral origin of the 



shoot, two spirals are constructed, 



each of which commences from one 



of the origmal orthostichies, and, so 



to speak, continues it in a spiral 



curve ; the one contains all the leaves with an even number, the other those with 



an uneven number ; the tw^o are homodromal, runnino- in the same direction round 



the stem. The bilateral origin of the shoot may be followed in this manner up to 



-Transverse section of a shoot of .l/oi;' St 



